Epic's Unreal Engine has been one of the top choices for developing high-end AAA titles for years now. Today, though, the company is making a massive break from its past business model and opening the engine up to a much wider audience of developers. As of right now, anybody can gain access to the full version of Unreal Engine 4 by subscribing to it for $19 a month, plus paying a five percent royalty on gross revenues from any games released.

While Epic has previously opened up limited, binary-level access to its engine through efforts like the Unreal Development Kit (UDK) and mod toolkits, the new subscription program gives the general public access to the Unreal Engine source code for the first time. Subscribers will be able to download the complete C++ source code directly from GitHub and modify or add to it to their heart's content. They can also post modifications online for others to use.

This is "not the secretive, elite approach we've taken in the past where [the source code] is only available to a few teams in strict secrecy," Epic cofounder Tim Sweeney said at an announcement event during GDC today. "With Unreal Engine 4, we hope to wipe the slate clean... This is a bold new step for Epic, but we think it's an appropriate one for the new shape of the game industry."

"Our whole business is structured to succeed only if developers succeed," he continued. "If a developer succeeds with the engine, we succeed."

Sweeney specifically cited the rise of platforms like iOS and the indie development community as instrumental in the creation of the new business model. In this new world of game development, it no longer makes sense to negotiate terms for full source code access only with major companies that can spend millions of dollars for the privilege. While previous steps like the UDK were decent mid-level solutions and led to the creation of some great games, Sweeney said the Unreal Development Kit never got quite the uptake the company wanted.

Subscribers to the engine will be able to develop on either PC or Mac and deploy to PC, Mac, iOS, and Android, with "more platforms to come." Sweeney said that users looking at the source code will see upcoming work on support for Linux and SteamOS, in addition to direct HTML5 deployments in the future. Subscribers will also get access to new support forums, video tutorials, and coding samples like the completely original Flappy Chicken.

The five-percent royalty applies to all revenues from a game's release, including direct sales, micro-transactions, and in-game ads. That fee also comes on top of any costs Apple, Valve, or any other platforms may take as their cut, so an Unreal Engine 4 game on iOS would see only 65 percent of its sales price go to the developer (Update: The original version of this story incorrectly stated the five percent fee was assessed after platform fees. Ars regrets the error). For developers who want to release completely free games or educators who want to poke around the code, the costs are limited to only $19 per month. That fee can be cancelled any time, with the developer retaining access to the existing code. But users will have to resubscribe to make use of the latest updates to the engine's codebase (and will still obviously be on the hook for the royalties regardless of subscription status).

During the announcement, Epic once again stressed the power of Unreal Engine 4 to build worlds easily without programming experience. Level designers can easily drop in objects complete with pre-programmed "blueprints" of how they interact with the world and other objects, or they can code their own behaviors using a graph-based interface that requires no knowledge of specific coding languages.

Unrelated to the engine, near the end of the presentation, Sweeney said that Epic is not currently working on a new Unreal Tournament title, focusing instead on the previously announced Fortnite.

Kyle Orland / Kyle is the Senior Gaming Editor at Ars Technica, specializing in video game hardware and software. He has journalism and computer science degrees from University of Maryland. He is based in the Washington, DC area.